The changes of magnetic properties in magnetite nanoparticles during two different stabilization processes were investigated. Magnetic nanoparticles (MNPs) were obtained by electrochemical synthesis from two kinds of salts: (CH3)4NCl and NaCl. After that, two methods-steric and electrostatic-were used to stabilize MNPs with oleic acid (OA) and sodium hydroxide (NaOH), respectively. As a consequence, aqueous and organic dispersions were obtained after surface modification. The coated nanoparticles were characterized by TEM, zeta potential, thermogravimetry analysis (TGA), cyclic voltammetry (CV), magnetization measurements, and infrared and Mössbauer spectroscopy. The results showed that the particles were between 8 and 13 nm in size. In addition, the MNPs were coated with negative charge layers from NaOH by physisorption and coated with carboxylate groups from OA by the chemisorption process, and hence, they exhibited different reactivity and behavior depending on the nature of the electrolyte used in the electrochemical synthesis. Furthermore, the uncoated and coated MNPs had a narrow size distribution. Additionally, the saturation magnetization values showed dependence on the magnetite synthesis conditions and surface modifiers.

No abstract

The formation of magnetite nanoparticles (Fe 3 O 4 -NPs) by electro-oxidation process was studied by in situ and ex situ techniques in chloride electrolytes with and without ethanol. The electrochemical synthesis is characterized by the application of a current disturbance that promotes the oxidation of a low carbon steel electrode in solution to an oxidized state (Fe 2+ ) which is subsequently transformed into magnetite by reactions in solution. The electrochemical synthesis results in a final product of pure and crystalline magnetite nanoparticles (20-40 nm). The presence of ethanol in the electrolyte does not modify the mechanism of magnetite formation but it extends the lifetime of some precursors during electrosynthesis and promotes the formation of low size magnetite nanoparticles. In situ Raman spectroscopy measurements were used in order to identify the precursor species formed prior to the formation of magnetite nanoparticles during the electro-oxidation of the low carbon steel in electrolyte containing chloride and ethanol. It was corroborated that the electrochemical synthesis of magnetite follows the sequence: Fe(OH) 2 → GR(Cl − ) → γ-FeOOH → Fe 3 O 4 , with a redox interaction between Fe(OH) 2 and γ-FeOOH precursors.

No abstract

No abstract